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Both Dodd and Wolk have claimed ads attacking each of them and paid for by outside organizations range from misleading to false. The ads try to paint Wolk as a flip-flopper and point to him voting to raise water rates without support from the community. The process, in fact, went through several local channels.

An ad hitting Dodd for approving a supervisorial pay raise omits entirely that salary boosts, as mandated by county ordinance, are pegged to local judges’ pay.

While Dodd also has worked to burnish his environmental credentials, Davis Mayor Joe Krovoza points to his growing list of supporters from that field, including the Sierra Club, California League of Conservation Voters and Clean Water Action.

Krovoza, a senior official at the University of California, Davis, has been trying to break through the paid messaging for the other Democrats.

The district for years has been safely Democratic. Prior to redistricting, it stretched across Yolo and Solano counties (and included West Sacramento), but was redrawn to take in Napa, Sonoma and Lake counties.

The Republicans running in the Democratic-favored 4th District include Charles Schaupp, a farmer and retired Marine Corps veteran.

Bill Dodd

Party: D

Biography: Dodd, 57, owned a Culligan water dealership for nearly two decades before being elected to the Napa County Board of Supervisors in 2001. He switched his party loyalty from the GOP more than a year ago, saying the Democratic Party better reflected his values on marriage equality, immigration reform and how to stem the shrinking of the middle class.

On the issues: Dodd believes high-speed rail should be scrapped unless a more realistic business plan emerges. He says any water bond that goes to voters should include at least $2.5 billion in water storage projects. He opposes marijuana legalization and says California’s current level of taxation is fine.

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Biography: Krovoza, 51, has served as mayor of Davis since 2011 and on the City Council since 2010. He worked two years as a water attorney after graduating from law school at UC Davis in 1994, and since 1996 has been the senior director for development and external relations and the UC Davis Institute of Transportation Studies and Energy Efficiency Center.

Key supporters: Sierra Club, Equality California and Ed Begley Jr.

On the issues: He supports high-speed rail but has major concerns about its implementation. He opposes the Delta tunnels and has called for both greater conservation efforts and more groundwater and off-stream storage capacity. He wants to observe Colorado and Washington before committing to marijuana legalization in California. He supports an oil extraction tax and higher tobacco taxes.

Website: joekrovoza.org

Charles Schaupp

Party: R

Biography: Schaupp, 59, retired after a 28-year career in Marine Corps, having served in Desert Storm in 1991 and Iraq in 2004. He has been a director in the Esparto Community Services District since 2012 and was a trustee in the Esparto School District from 1993 to 2000.

On the issues: He opposes the high-speed rail and water tunnel projects. He supports building full-service dams for water storage, flood control and hydroelectric power. He supports more regulation of medical marijuana and opposes recreational marijuana. He says California’s taxes are too high and would focus on paying down debt.

Website: charlieschaupp.com

Dan Wolk

Party: D

Biography: Wolk, 36, has served on the Davis City Council since 2011. In Solano County, he is a deputy county counsel for public finance, public contracting and water issues. He founded the Legal Clinic of Yolo County.

On the issues: Wolk supports the high-speed rail project. He opposes the plan for twin water tunnels, and supports more storage, increased conservation efforts and desalinization. He supports medical marijuana but wants to see the results in other states before endorsing legalization for recreational use. Wolk supports an oil tax, eliminating the requirement for a two-thirds vote to increase taxes and creating a “split roll” to tax commercial properties differently than residential property.